Abstract

The flow in a plane channel with two idealized stents (one Λ-shaped, the other X-shaped) is studied numerically. A periodic pressure gradient corresponding to one measured in the left anterior descending coronary artery was used to drive the flow. Two Reynolds numbers were examined, one (Re = 80) corresponding to resting conditions, the other (Re = 200) to exercise. The stents were implemented by an immersed boundary method. The formation and migration of vortices that had been observed experimentally was also seen here. In the previous studies, the compliance mismatch between stent and vessel was conjectured to be the reason for this phenomenon. However, in the present study we demonstrate that the vortices form despite the fact that the walls were rigid. Flow visualization and quantitative analysis lead us to conclude that this process is due to the stent wires that generate small localized recirculation regions that, when they interact with the near-wall flow reversal, result in the formation of these vortical structures. The recirculation regions grow and merge when the imposed waveform produces near-wall flow reversal, forming coherent quasi-spanwise vortices, that migrate away from the wall. The flow behavior due to the stents was compared with an unstented channel. The geometric characteristics of the Λ-stent caused less deviation of the flow from an unstented channel than the X-stent. Investigating the role of advection and diffusion indicated that at Re = 80 advection has negligible contribution in the transport mechanism. Advection plays a role in the generation of streamwise vortices created for both stents at both Reynolds numbers. The effect of these vortices on the near-wall flow behavior is more significant for the Λ-stent compared to the X-stent and at Re = 200 with respect to Re = 80. Finally, it was observed that increasing the Reynolds number leads to early vortex formation and the creation of the vortex in a stented channel is coincident with the near wall flow reversal in an unstented one.

Received 09 March 2013Accepted 20 August 2013Published online 27 September 2013

Acknowledgments:

We would like to thank Dr. Matthew David Ford for performing the calculations on OpenFOAM and for his valuable comments on the results. U.P. and A.R. were partially supported by the National Science and Engineering Research Council (NSERC). U.P. also acknowledges the support of Canada Research Chairs program. We also thank the High Performance Computing and Virtual Laboratory (HPCVL), Queen's University site (www.hpcvl.org), for the computational support.

Article outline:I. INTRODUCTIONII. PROBLEM FORMULATIONIII. RESULTSA. Flow descriptionB. Flow behavior with and without stentC. The role of advectionD. Vortex creation and migrationIV. CONCLUSIONS